Yearly in the United States over 500,000 newborns are delivered prematurely. This population is at high risk of catastrophic bowel disease known as necrotizing enterocolitis. Infants with necrotizing enterocolitis are at high risk of death, and survivors are at increased risk of mental retardation. Metronidazole is an antibiotic that is often administered to infants with suspected or confirmed necrotizing enterocolitis. Unfortunately, the appropriate dose of metronidazole in premature infants has not been established and it is likely to be different from older children and adults.